The present invention relates to an antenna feed device which provides two-axis tracking by use of first and second sum waveguide channels and one difference channel. A polarizing section is rotatably mounted to rotate the polarization of a wave by a factor of two, that is, the polarization of a wave will be rotated 90.degree. when the polarizing section is rotated 45.degree. and, likewise, the polarization of a wave will be rotated 180.degree. when the polarizing section is rotated 90.degree..
The resolution of early tracking radars was improved by raising the transmitter frequencies, but along with this improvement came the disadvantage of receiving precipitation clutter. Circularly polarized electromagnetic energy appears to be the most promising technique to reject clutter caused by raindrops. Radars are now in use which are capable of producing, selectively, either linear or circular polarization of electromagnetic energy. Circular polarization technique is based on the assumption that raindrops are symmetrical and objects of desired detection are asymmetrical. In these systems, circularly polarized energy of one direction of rotation is transmitted and the energy reflected by symmetrical raindrops will reverse the direction of rotation and these returns will be rejected by the circularly polarized antenna.
In the invention filed in the United States Patent Office by Begeman et al. on July 14, 1964, Ser. No. 384,029, now Pat. No. 2,453,617, entitled, "Switchable Linear-Circular Polarized Monopulse Radar Feed Producing Two Axis (Three-Dimensional Tracking) Information Utilizing A Two-Lobe Monopulse Design," a two-lobe monopulse antenna feed is used to obtain two-axis elevation and aximuth range tracking information, the same as obtained from a four-lobe antenna feed. The antenna feed consists of a folded-tee or comparator and a circularly polarizing component which may be used to switch from linear polarization to right or left circular polarization, as desired. The circularly polarized waves are produced for transmission by conducting linearly polarized energy of the rectangular waveguide TE.sub.10 mode from a sum channel of the transmitter through a folded-tee or microwave comparator section to a circular waveguide to convert the energy to the circular waveguide TE.sub.11 mode. The circular waveguide is rotatable on the folded-tee and has two rods placed diametrically across the guide in the same plane and spaced 3/8 wavelength apart to produce a 90.degree. differential phase shift when the electric fields are parallel to the rods.
The invention field in the United States Patent Office by applicant on Dec. 22, 1965, Ser. No. 515,740, entitled, "3-Channel Selectable Polarization, Target Discrimination Antenna," improved on the previous referenced application of Begeman et al by adding a coupling pin or probe, between the comparator ports and the polarizer, for the purpose of receiving that energy which is cross-polarized with respect to the polarization of the transmitting sum arm. This constituted a great stride in radar art by enhancing the ability to identify different types of targets and to detect hidden targets in rough terrain, forests, underbrush and rough seas. The invention may also be used in a passive system as a radar detector wherein the polarization of received energy may be linear, elliptical, or either rotation of circular.